Remove command-line option inconsistencies

Optional arguments, as parsed by the getopt_long mechanism, are
inherently inconsistent with how you define required arguments.

To avoid confusion we decide to avoid this inconsistency by replacing
optional options with additional options with required argmuments.

src/options.h

@@ -33,6 +33,7 @@ enum timestamp_t
     TIMESTAMP_24HOUR_START,
     TIMESTAMP_ISO8601,
 };
+
 const char* timestamp_token(enum timestamp_t timestamp);
 enum timestamp_t timestamp_option_parse(const char *arg);